The present invention relates to an image recording apparatus, which is provided with an automatic document conveyance means by which a double-sided document can be read, and by which double-sided copying can be performed. Specifically, the present invention relates to an image recording apparatus having a non-stacking type automatic reversing unit.
Recently, copiers of superior copy productivity and operability are being provided on the market. The automatic document conveyance means automatically conveys a document, which is conventionally manually placed one by one in the exposure position on a platen, to the exposure position. An image is formed synchronously with the automatic document conveyance operation to the exposure position. However, due to the spread of digitizing technology and reduction of memory cost, copying operations can now be performed without depending on operations of an automatic document conveyance means, as follows. A memory (an image memory section) is provided in the apparatus; documents are conveyed one by one by an automatic document conveyance means to the exposure position; document information on the exposure position is read by a reading means having a photoelectric conversion means such as a CCD; all the document information is temporarily stored in the memory and image information on the specific page is read from the memory at the time of image formation. Conventionally, when a plurality of copying volumes are copied from a plurality of documents, the automatic document conveyance means circulates the documents plural times so that a plurality of copied volume are obtained. However, when a so-called electronic RDH stored in the memory is adopted in the apparatus, the above described operations are no longer necessary.
Further, recently, many copiers having double-sided copying functions are being provided on the market. That is, automatic document conveyance means by which double-sided documents can be read are provided. On the other hand, relating to copiers, an automatic reversing unit (ADU) is provided in a copier, single-sided copied transfer sheets are not delivered outside the apparatus, and transfer sheets are reversed and conveyed by the ADU in the apparatus, copying of the other side is carried out, and after double-sided copy has been completed, the transferred sheets are delivered outside the apparatus. Relating to ADUs, the following types are provided: a stacking type ADU in which a stacker is provided in the apparatus, and after the transfer sheet, one side of which has been copied, is temporarily stacked on the stacker, the other side is copied; and a non-stacking type ADU in which no stacker is provided in the apparatus, and only a reversing conveyance path is provided. Although the stacking type ADU and the non-stacking type ADU have respective advantages and disadvantages, the non-stacking type ADU has better copy productivity for the electronic RDH.
As described above, image information is stored in a large capacity memory, and can be read from the memory as necessary. Although the non-stacking type image recording apparatus has better copy productivity (in terms of the number of copied sheets per unit of time) than conventional methods of double-sided copying, it was clearly found that copy productivity could be improved still further in following points after further investigation.
In the non-stacking type image recording apparatus, the maximum conveyance number of transfer sheets, which can exist in the reversing path in the reversing section, is determined depending on the apparatus, and when the maximum conveyance number of the transfer sheets is assumed to be one cycle, image processing is carried out per cycle. When a plurality of copying volume are copied, one copying volume has been completed such that only remaining copying sheets of the transfer sheets, which exceed the maximum conveyance number while one copying volume is outputted, are conveyed, and in the next copying cycle, the transfer sheet is conveyed from the first page of image data of the copying volume. This is shown in prior art in FIG. 10(B). In FIGS. 10(A), 10(B) and 10(C), the maximum conveyance number per cycle is 3, and 8 pages image data are outputted.
Further advantages of this stackless (non-stacking) type apparatus is as follows. The transfer sheets are always nipped by conveyance rollers, and therefore jamming frequency is greatly reduced. The transfer sheets are continuously fed and conveyed, and therefore the copy productivity is not decreased.
However, the following are problems caused by the stackless type apparatus. The front and the rear surfaces of the transfer sheets are continuously processed by feeding.fwdarw.image formation.fwdarw.reversed circulating.fwdarw.image formation.fwdarw.sheet delivery, and therefore, when a transfer sheet is delayed in the conveyance path from the sheet feed section, or in the circulating reversing sheet feeding path, the reliability of control of the conveyance path or circulating reversing sheet feeding path is deteriorated, in such a manner that the succeeding transfer sheet catches up with the preceding transfer sheet, or the like.